Asphalt compositions



Unite ABSTRACT OF THE DISCLOSURE An improved asphalt compositioncomprising 1 to 20 weight percent atactic propylene-ethylene copolymercontaining 1 to 30 Weight percent ethylene and having a molecular weightin the range of 10,000 to 40,000 and 80 to 99 weight percent asphalt.

This invention relates to improved asphalt compositions and particularlyto paving asphalt containing a small but effective amount of amorphouslow molecular weight propylene-ethylene copolymer. Paving grade asphaltis made from residuum stocks originating with such crudes as Mid-Continent, Wyoming, West Texas, Mexican, Middle East and Venezuelan. Atthe present time, the majority of asphalt crudes are treated by eitherof two processes, i.e., straight vacuum reduction and vacuum reductionfollowed by air blowing to produce suitable residuum. The method used isdependent on the source and nature of the crude. For example, mostVenezuelan crudes are treated by vacuum distillation alone whereasMiddle East crudes generally require vacuum distillation followed by anair blowing treatment.

State and federal governments have derived paving asphalt specificationswhich must be met where the material is to be used in public roadbuilding programs. The requirements vary in the different jurisdictionsbut all require a certain specification to be met for penetration. Inthe broadest sense, paving asphalt may have a penetration range of 40 to300 but the great majority of asphalt paving put down has a penetrationof 70 to 120 at 77 F. Over 40% of the asphalt used in the MiddleAtlantic States is 85/100 penetration grade. This means that thepenetration at 77 F. must fall Within the range of 85 to 100.

The penetration test determines the hardness or softness of thematerial. Degrees penetration means the distance (in of a centimeter) astandard needle will penetrate into the asphalt when loaded to 100 gramsfor five seconds at 77 F. Penetration is also measured at 39.2 F. with a200 gram weight and a time of 60 seconds. These tests are made accordingto ASTM D561 procedure. Another specification that ordinarily must bemet by paving grade asphalt compositions is penetration ratio.Penetration ratio is Pen. 392 F.

Pen. 77.0 F.

and is multiplied by 100 to express the value as a percentage. Normallymost states and federal specifications require paving grade asphalt tohave a penetration ratio of at least 30 percent.

It is necessary to exercise very careful control in the reduction ofcrude to a certain percentage residual bottoms and in air blowing tomeet these paving grade specifications.

A number of polymers and copolymers have been added to asphalts toimprove such properties as softening point, penetration, penetrationratio, and ductility. The success of these materials has been limited.The chief reasons for lack of success are high cost, poor dispersibilityStates Patent 3,395,110 Patented July 30, 1968 employing conventionalblending equipment, and poor low temperature performance.

It has recently been discovered that by the addition of certain olefinhomopolymers asphalt can be produced which will meet the abovepenetration requirements without subjecting the asphalt to the costlyair blowing treatment. However, all of these improved asphaltcompositions suffer from the inherent defect of poor low temperatureflexibility. It has been found that at sub-freezing temperatures,particularly in moisture-rich areas, most of the presently used asphaltcompositions become brittle and are subject to cracking and crumbling,consequently permitting only a limited period of use before repairs orreplacement is necessary.

It is an object of this invention to provide an improved asphaltcomposition having superior low temperature flexibility.

It is a particular object of this invention to provide an improvedpaving grade asphalt composition which meets all the requirements ofpaving grade asphalts while exhibiting superior sub-freezing wear-liftqualities due to its improved low temperature flexibility.

I have found that certain amorphous copolymers of propylene provide thequalities lacking in other polyolefinasphalt compositions. Thesecopolymers are the soluble by-products produced in the preparation ofpropylene ethylene copolymers.

It is known that some of the deficiencies of isotactic polypropylene,which is highly crystalline, can be overcome by inserting ethylenesegments of limited size and quantity in the propylene polymer chain.During the preparation of the crystalline propylene high molecularweight polymers and copolymers a certain amount of substantiallyamorphous low molecular weight material is produced. This material isnormally soluble in the inert hydrocarbon polymerization medium and isnormally considered an undesirable by-product of the process. Thepolymerization process from which the low molecular weight amorphouspropylene-ethylene copolymer by-product useful in the present inventionis obtained is as follows:

A highly crystalline propylene-ethylene copolymer is prepared bycontacting under temperatures, pressures, polymerizing conditions, andin the presence of coordinate complex catalyst systems such as thosedisclosed in British Patents 889,230 and 889,659, an olefin mixtureconsisting of a major amount of propylene (i.e., -99 wt. percent) and aminor amount of ethylene (i.e., 1-20 wt. percent). Polymers havinghighly crystalline structure by X-ray analysis can be prepared in theabove-described manner. The polymerization product generally containssome amount of predominately low molecular weight amorphous or atacticpolymers which are more soluble in hydrocarbon solvents than thecrystalline polymers and hence can be separated therefrom, for example,by extraction with pentane at room temperature. This hydrocarbon solubleby-product of the above disclosed copolymer process which usuallycomprises 2 to 30% of the total polymer product and normally has anaverage molecular weight in the range of 10,000 to 40,000 as measured byintrinsic viscosity is recovered from the insoluble product by variousmeans. In one known process the total polymerization product andcatalyst in the hydrocarbon polymerization medium is contacted with asolvent consisting of methanol and water to kill the catalyst. Thecatalyst is then removed in solution with the methanol and water'leavingbehind a hydrocarbon slurry of soluble and insoluble polymer product.The soluble copolymer and hydrocarbon are removed from the insolublecopolymer product by filtering or centrifuging. The soluble copolymer isrecovered from the hydrocarbon solvent which is subsequently recycled.The

material which remains is the predominately low molecular weight (10,000to 40,000) substantially amorphous propylene-ethylene copolymer employedin the composition of this invention. For purposes of this inventionthis hydrocarbon soluble propylene-ethylene copolymer is hereinafterreferred to as atactic propylene-ethylene copolymer or as the heptanesoluble fraction of the propylene-ethylene copolymer.

The atactic propylene-ethylene copolymer used in the present inventionis predominately propylene having short segments of ethylene randomlydispersed within the propylene polymer chain. The copolymer is normallysoluble in heptane and is predominately amorphous although it issynthesized using a stereospecific catalyst system.

Because of the fact that lower molecular weight fractions ofpropylene-ethylene copolymers have higher concentrations of ethylenethan the higher molecular weight fractions of the same copolymer, theheptane soluble fraction can contain as much as 30 weight percentethylene even though the weight percent ethylene in the monomer feedduring polymerization is much lower. For present purposes the atacticcopolymer should contain from 1 to 30 weight percent ethylene.

The copolymer product of the present invention is termedpropylene-ethylene copolymer to denote the fact that the polymer ispredominately polypropylene with short segments of ethylene randomlydispersed in the propylene polymer chain. The copolymers of the presentinvention may be readily distinguished from ethylenepropylene blockcopolymers which are characterized as high molecular weight copolymerssynthesized by nonstereospecific catalyst systems which copolymers havehigh concentrations of long ethylene sequences in the copolymer chain.These block ethylene-propylene copolymers, because of their distinctdiflerences in molecular structure, weight and high ethyleneconcentration, are readily distinguished from the copolymers of thepresent invention.

The coordinate complex catalyst referred to in the copolymerpolymerization above can be a metal subhalide of a Group IVa, Va, or VIa(of the periodic table as set out on page 411 of the PartingtonsTextbook of Inorganic Chemistry, MacMillan & Co., Ltd., London, 1937)metal in combination with a polymerization activator. By the termactivator is intended a co-catalyst as shown in Table XII-2 and TableXII-4 in Linear and Stereo Regular Addition Polymers, by Norman G.Gaylord and Herman F. Mark, copyrighted in 1959 by IntersciencePublishers, Inc.

In the present invention the amount of atactic propylene-ethylenecopolymer mixed with the asphalt is small, preferably in the range offrom about 1 to by Weight. Any suitable mixing method can be used whichresults in good distribution of the polymer in the asphalt.

A coordinated catalyst system comprising titanium trichloride anddiethyl aluminum chloride was used in the synthesis of the atacticpropylene-ethylene copolymer which forms a part of the specificembodiments of the present invention disclosed below. For use in thepresent invention, the heptane soluble fraction of the propyleneethylenecopolymer obtained by contacting under anhydrous conditions a monomermixture of 3.5 weight percent ethylene and 96.5 weight percent propylenewith the above mentioned coordinate complex catalyst dispersed inheptane at a temperature of 150 F. and at a pressure of 65 p.s.i.g. isrecovered by previously discussed methods.

This atactic propylene-ethylene copolymer is typically characterized asbeing white and translucent having a specific gravity of 0.86 (ASTMD162259T), a ring and ball softening point at 120 C. (ASTM D28*58T), abrittle point of C. (ASTM D-146-58T), and molecular weight of about25,000 as determined by intrinsic viscosity measurements.

The above described propylene-ethylene copolymer is blended withLagomedio asphalt bottoms in the concentration range of 2 to 10 weightpercent copolymer to form a paving grade asphalt.

In Table I is demonstrated the improvements in penetration properties ofLagomedio asphalt that are achieved by addition of incremental amountsof atactic propyleneethylene copolymer.

As is readily apparent from the data of Table I, the most stringentpenetration specifications of paving grade asphalt can be easily met bythe practice of the present invention.

However, the most significant improvement realized by the paving asphaltcompositions of the present invention lie in the superior lowtemperature flexing properties as demonstrated by the data presented inTable II. A paving asphalt composition having 10 weight percent atacticpropylene-ethylene copolymer blended therein is shown to have superiorlow temperature flexing properties when compared with two presentlyknown paving asphalt compositions.

A new asphalt composition having a flexural modulus at 20 F. in therange of 300-1500 p.s.i. has been discovered. This new compositioncomprises a blend of asphalt and substantially amorphous atacticpropyleneethylene copolymer containing 1-30 weight percent polymerizedethylene and 99-70 weight percent polymerized propylene. The copolymeris obtained as the heptane soluble fraction of the stereospecificpolymerization of a propylene-ethylene monomer mixture. The content ofthe copolymer in the asphalt-copolymer composition can be in the rangeof 1-20 weight percent of the blend.

This improved low temperature flexibility of the compositions of thepresent invention is totally unexpected in view of the results notedwhen the atactic homopolymer of propylene is blended with asphalt. As isclearly demonstrated by the results in Table II, the addition of atacticpolypropylene to asphalt results in an asphalt composition having ahigher resistance to flexing at 20 F. than unadulterated asphalt. Poorlow temperature flexing properties render the atactic polypropylene,asphalt composition undesirable for many applications, particularly incold climates. However, an asphalt containing atactic propylene-ethylenecopolymer is found to have superior low temperature flexing propertiesover both unadulterated asphalt and an atactic polypropylene-asphaltcomposition.

Low temperature stiffness or lack of flexibility is a primarycontributor to cracking and subsequent deterioration of roads,particularly in areas subject to colder climates. Thus it can be seenthat the paving compositions of the present invention by their superiorflexibility at low temperatures are more resistant to cracking andresulting deterioration of asphalt road surfaces than other presentlyused asphalt paving compositions. The asphalt paving compositions of thepresent invention by virtue of their superior flexibility propertiesinherently possess superior wear properties, particularly in colderclimates.

The atactic propylene-ethylene copolymer can be used according to thepresent invention in conjunction with any crude asphaltic residium. Theinvention is particularly useful for those residuua which are diflicultto bring into paving grade specifications by conventional procedures.

The invention has been described primarily with references to asphaltsfor use in paving; however, the composition of the present invention mayfind equal utility where an asphalt having particular penetrationcharacteristics is required. For example, the asphalt compositions ofthe present invention may be used in soil stabilization, protection ofbanks and canals by asphalt linings, pipe coating and coating of metalswhich are to be buried in soil, and moulded articles such as batteryboxes and tiles.

Obvious modifications such as blending of the asphalt composition of theinvention with mineral aggregates,

6 cement, sand, asbestos, vermiculite, fiber glass and the 5. A blendaccording to claim 3 having a flexural modlike are included in the scopeof the invention. ulus at 20 F. in the range of 300 to 1500 p.s.i.

TABLE I 6. A method for improving low temperature properties of asphaltwhich comprises blending with said asphalt Lagornedio Bottoms, WeightPercent 100 98 94 92 90 Awctichpligpymggthylene copolymer, 6 8 10 5 from1 to weight percent atactic propylene-ethylene eig t ercent 0 2penetration 3 F dmm 24 33 34 35 34 copolyl'nier contan'llng to 30 welghtRel-cent ethylene llzenegragon t 1%, g n m. 1% polymerized therem, Saidcopolymer having been recovene a M ered from the stereospecificpolymerization of a propylene- TABLE II ASTM D-28-58'l ASTM D790-61Paving Composition Pen. at Pen. at Pen. Duct. Softening Point, 77 F.39.2 F. Ratio at 77 F. Flexural Modulu F, psi. at 20 F.

100% Lagomedio Bottoms 106-110 131 24 18 100+ 1, 779 10 Wt. fiercentAtactic Polypropy ene 90 Wt. Percent Lagomedio 138 57 19 33 21 747Bottoms 10 X5 liercegt Atlactic Propyleney ene opo ymer 90 Wt. PercentLagomedio 142 62 34 54 58 689 Bottoms l l i ethylene monomer mix andhaving a molecular weight in 1. A composition comprising 1 to 20 weightpercent th rang ilf1 fl atactic propylene-ethylene copolymer having 1 to30 7. A method for improving penetration properties of weight percentethylene therein and having a molecular asphalt which comprises blendingwith said asphalt from weight in the range of 10,000 to 40,000, and 80to 99 l to 20 weight percent atactic propylene-ethylene copolyi hpercent h lt, mer containing 1 to weight percent ethylene polymer- 2. Asa new composition a blend of asphalt and atactic ized therein, saidcopolymer having been recovered from propylene-ethylene copolymerrecovered from a stereothe stereospecific polymerization of apropylene-ethylene specific polymerization of a propylene-ethylenemonomer 30 monomer mix.

mixture said propylene being in the range of 70-99 weight 8. Acomposition according to claim 1 having a flexpercent and said ethylenebeing in the range of 1 to 30 ural modulus at 20 F. in the range of 300to 1500 psi.

weight percent of the polymerized copolymer product, 9. A compositionaccording to claim 2 having a flexural said copolymer having a molecularweight in the range of modulus at 20 F. in the range of 300 to 1500 psi.

10,000 to 40,000 and said blend containing 1 to 20 weight 10. A methodaccording to claim 9 wherein the impercent copolymer therein. provementin penetration properties comprises lowering 3. As a new composition, ablend of asphalt and subthe penetration value of the asphalt compositionat 77 stantially amorphous atactic propylene-ethylene copoly- F. andraising the penetration value of the asphalt commer containing 1 to 30weight percent polymerized ethylposition at 392 F.

ene and 99 to 70 weight percent propylene polymerized therein obtainedas the heptane soluble fraction of the References fiited stereospecificpolymerization off a propyltlene-ethglene UNITED STATES PA ENTS monomermixture, the content 0 said copo ymer eing in the range of 1 to 20weight percent of the blend and g g et figg ggg ggg a molecular Weghtthe range 3:154:508 10/1964 Clelland 260-28:5

4. A paving composition comprising 80 to 99% asphalt and 1 to 20% of asubstantially amorphous atactic propylene-ethylene copolymer having 1 to3 0 weight percent JULIUS FROME Primary Examiner. ethylene polymerizedtherem and having a molecular weight in the range of 10,000 to 40,000.H. S. KAPLAN, Assistant Examiner.

